along similar lines
Iíve got an 88 560SL which I just bought and she runs quite well. The one drivability issue that I have is one Iíve seen on several older cars that Iíve owned related to the transmission. When the car is driven from 40 Ė 50 mph, then slowed to 20 mph or so to take a turn, when I go back on the gas pedal, the transmission has a bit of a jerk as it downshifts from 4th to 3rd . The downshift appears to happen slowly, but is not soft. When Gisela decides that she is going to downshift, she does. This happens fast enough that the rpms donít rise, so I donít think that Iím burning up anything yet, but I need to get this squared away before I cook any internals.
The service point that Iím going to begin with is replacing the VAC line from the modulator to wherever it pulls from on the manifold. Things are rather warm under the bonnet with that hunk of aluminum under there, and lots of rubber needs to be replaced. I can see this hose easily being cracked and leaking. If that fixes it, thank god. If not, Iíll have my independent adjust the modulator, which leads me to the big question. Do I have the fluid and filter changed?
There is one school of thought on this matter with late 60s Mustangs that says leave well enough alone if you havenít been doing 30K mile changes in the past. Iím at 90K, and donít have a good service history - older lady was previous owner, and while it appears that the dealers took care of things, I canít be sure of what happened. Without regular fluid changes and a fresh supply of detergent additives in the new oil, things have become ďseasonedĒ in the old transmission, and as long as the fluid isnít burned, it is fine. I have seen a perfectly good C-6 trans. behind a 351 Cleveland go from fine to rebuild immediately after a fluid change. The shop had us look at the ďnewĒ fluid when they pulled the tranny. It was dark and the pan and filter had lots (2 Ė 3 table spoons) of sediment looking stuff that wasnít there 2 weeks prior when we dropped the pan to replace the filter. They said that the new fluidís detergents worked so well that they stripped that trans. clean inside, which unfortunately led to itsí demise. The sediment was what was clinging to seals and assisting keeping the tranny tight. When we looked at the bands and clutch packs, they were in good shape and could have gone for years had we not changed the juice.
Has anyone seen the failure after fluid change scenario with these 4-speed autos? All the other shifts are so smoooooth, I hate to mess with it.
As a side line, are there specific VAC lines that are likely culprits for the center A/C vents not opening? Rest of system works fine. Any rubber parts under the hood that should be replaced (outside of the usual suspects) that I should look for? I already replaced the little black rubber caps on the brake fluid reservoir vents - $6 each Ė welcome you MBZ!